An ultrasound imaging apparatus has included a transducer array that transmits an ultrasound beam into an examination field of view. As the beam traverses structure (e.g., of a sub-portion of an object or subject) in the field of view, sub-portions of the beam are attenuated, scattered, and/or reflected off the structure, with some of the reflections (echoes) traversing back towards the transducer array. The transducer array receives and processes the echoes, and generates one or more images of a sub-portion of the subject or object. The one or more images are visually displayed.
Ultrasound imaging has also been used to visualize an instrument disposed in or being disposed in the object or subject. For example, ultrasound imaging has been used to produce images of a needle being positioned in a subject and to verify positioning of the needle tip for a medical procedure. Unfortunately, the image quality of the needle in the images tends to be low, e.g., due to the low signal to noise ratio of the ultrasound images and speckle. Approaches to improve visualization of a needle have included beam steering and needle shaft tracking with a tracking device on the instrument.
Beam steering has included steering the beam so that the direction of the beam is perpendicular to the instrument being visualized (e.g., the shaft of a needle), which improves image quality of the instrument. However, since the position and angle of insertion of the instrument is unknown, the ultrasound beam is steered over a wide range of angles to cover multiple possible scenarios in an attempt to find a suitable angle. Unfortunately, steering the beam to cover a wide range of angles may introduce artifacts into the images, such as false enhancement on strong tissue interfaces.
With needle shaft tracking, an electro-magnetic device(s) has been affixed to a handle of the instrument or the needle tip, and the device is calibrated so that signal received by the device(s) indicates the location/angle of the device and can be used to predict the location and orientation of the needle. With the device affixed to the handle, any bending of the needle shaft introduces error between the predicted location and the actual location of the needle tip. Having the device affixed to the needle tip mitigates this error. Unfortunately, it also requires a custom-made needle, which adds cost and limits which needles can be used.